Aromatic polyamide fibers are known to be useful in the preparation of high temperature resistant protective clothing. Poly(m-phenylene isophthalamide) fibers have been found to be particularly desirable since they provide fabrics having good aesthetic properties. The wearing of such protective clothing is thus made less burdensome and the needed protection is provided against a perhaps unlikely exposure to high temperature. However, fabrics comprised of 100% by weight poly(m-phenylene isophthalamide) fibers do not provide the needed protection against extreme temperature conditions such as that provided by exposure to burning fuel. Under such exposure, fabrics of 100% by weight poly(m-phenylene isophthalamide) fibers break open, thus exposing the wearer's skin to the flame. Satisfactory resistance to such fabric break-open is provided by an intimate blend of 3-20% by weight of poly(p-phenylene terephthalamide) fibers with poly(m-phenylene isophthalamide) fibers. Although this fabric provides adequate resistance to break-open, the fabric shrinks so much on total immersion of the wearer in flames that the fabric is drawn down snugly against the wearer's skin, thereby expelling the insulating air layer otherwise present. This allows conductive heat transfer so that the wearer sustains more severe burns than would occur with the layer of insulating air present. In order to avoid loss of the insulating air layer, a fabric of about 4 to 5 oz./yd..sup.2 should shrink no more than 5% under the conditions of exposure. Military specifications require such a shrinkage limitation. The most preferred fabric weight is 4.5 oz./yd..sup.2.
Synthetic organic fibers are known which are inherently non-flammable and in fabric form shrink less than 5% on exposure to conditions simulating burning fuel. For example, a cured novolac resin fiber "Kynol" and poly(p-phenylene terephthalamide) fibers are such low shrinkage fibers. However, fabrics prepared exclusively from such fibers are not fully satisfactory because of poor fabric aesthetics and other problems.
Blends of high shrinkage and low shrinkage fibers are known to provide high fabric shrinkage even when only small amounts of high shrinkage fiber are present. For example, it can be seen from FIG. 3, page 549 of Man-Made Textile Encyclopedia, that as few as 20% high shrinkage fibers provides a fabric having very high overall shrinkage. Thus it would not be expected that an intimate blend of high shrinkage and low shrinkage fibers containing a relatively large amount of high shrinkage fibers could be used to prepare a low shrinkage fabric.
This invention provides an intimate blend of aromatic polyamide staple fiber components which in fabric form have desirable aesthetic properties and an overall fabric shrinkage of 5% or less when exposed to conditions simulating burning fuel.